JP2010506506A - Handover of a target base station to an arbitrary cell in a wireless communication system - Google Patents

Abstract

Techniques for performing user equipment (UE) handover in a cell-to-base station manner are described. The UE may receive a handover command that performs a handover from the source base station to the target base station. The source base station sends the context information of the UE to the base station. This context information is available for all cells of the target base station. The UE may attempt a handover from the serving cell of the source base station to the first cell of the target base station. The UE may attempt a handover of the target base station to the second cell if the handover to the first cell fails. The UE may either (i) receive the first cell and the second cell from the source base station, or (ii) receive only the first cell from the source base station and based on the broadcast system information Two cells can be determined.

Description

  The present disclosure relates generally to communication, and more particularly to techniques for performing a handover in a wireless communication system.

  Wireless communication systems are widely deployed to provide various communication content such as voice, video, packet data, messaging, broadcast, and the like. These wireless systems can be multiple access systems that can support multiple users by sharing available system resources. Examples of such multiple access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal FDMA (OFDMA) systems, and single carrier FDMA ( SC-FDMA) system.

  A wireless communication system may include any number of base stations that support communication for any number of user equipments (UEs). Each base station can provide communication coverage for a particular geographic region. The entire coverage area of each base station may be divided into multiple (eg, three) smaller areas. The term “cell” can refer to the smallest coverage area of a base station and / or base station subsystem that serves this coverage area.

  A UE (eg, a cellular phone) can communicate with a serving cell for a call. The UE may be mobile. And it can move from the effective range of a service providing cell to the effective range of a new cell that provides better service to the UE. The UE can perform a handover from the serving cell to the new cell. Handover to a new cell may fail for various reasons. In this case, the UE may lose connection with the serving cell and enter an idle state. The UE can then attempt to access the appropriate cell in the normal manner (eg, from the beginning) in the idle state. However, in the case of a handover failure, entering the idle state of the UE may result in service disruption. This is not desirable.

  This application is a U.S. provisional application 60 / 828,010 filed on October 3, 2006, assigned to the assignee of the present application and incorporated herein by reference, and October 4, 2006. Claims priority to filed US Provisional Application No. 60 / 828,186.

  This specification describes a technique for performing UE handover in a cell-to-base station scheme in order to improve handover reliability. The UE may receive a handover command that performs a handover from the source base station to the target base station. As part of the handover, the source base station sends the context information of the UE to the target base station. The target base station uses this context information to serve the UE after handover. This context information is available to all cells of the target base station without having to transfer another context from the source base station.

  In one design, the UE may attempt a handover from the serving cell of the source base station to the first cell of the target base station. The UE may attempt a handover of the target base station to the second cell if the handover of the target base station to the first cell fails. In one design, the UE may receive a first cell and a second cell from a source base station, eg, via a handover command. In another design, the UE may receive only the first cell from the source base station and determine the second cell based on system information (eg, a neighbor cell list) broadcast by the source base station. it can.

  Various aspects and features of the disclosure are described in further detail below.

FIG. 1 shows a wireless multiple-access communication system. FIG. 2 shows the configuration of cells on two frequencies. FIG. 3 shows a state diagram of the UE. FIG. 4 shows a message flow for UE handover from the source base station to any cell of the target base station. FIG. 5 shows a message flow for UE handover from a source base station to any cell of the target base station. FIG. 6 shows the message flow for the handover of the UE from the source base station to any cell of the target base station. FIG. 7 shows a process for performing a handover by the UE. FIG. 8 shows an apparatus for performing a handover by a UE. FIG. 9 shows a process for supporting UE handover by a source base station. FIG. 10 shows an apparatus for supporting UE handover by a source base station. FIG. 11 shows a process for supporting UE handover by a target base station. FIG. 12 shows an apparatus for supporting UE handover by a target base station. FIG. 13 shows a block diagram of a UE and two base stations.

  The handover techniques described herein may be used for various wireless communication systems such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and other systems. The terms “system” and “network” are often used interchangeably. A CDMA system may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includes wideband CDMA (W-CDMA) and low chip rate (LCR). cdma2000 covers IS-2000, IS-95, and IS-856 standards. A TDMA system may implement a radio technology such as Global System for Mobile Communications (GSM). The OFDMA system includes, for example, Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash OFDM (registered trademark) ) Etc. can be implemented. UTRA, E-UTRA and GSM are part of Universal Mobile Telecommunication System (UMTS). 3GPP Long Term Evolution (LTE) is the latest version of UMTS that uses E-UTRA, which uses OFDMA on the downlink and SC-FDMA on the uplink. UTRA, E-UTRA, GSM, UMTS and LTE are described in documents from an organization named “3rd Generation Partnership Project” (3GPP). cdma2000 and UMB are described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). These various radio technologies and standards are known in the art. For clarity, certain aspects of these techniques are described below for LTE, and the term LTE is used in much of the description below.

  FIG. 1 shows a wireless multiple-access communication system 100 with multiple evolved NodeBs (eNBs). For simplicity, only two eNBs 110a and eNBs 110b are shown in FIG. An eNB is a fixed station used for communication with a UE, and may also be referred to as a NodeB, a base station, an access point, or the like. Each eNB 110 provides communication coverage for a specific geographic region 102. In order to improve system capacity, the eNB coverage area may be divided into a plurality of small areas such as, for example, three small areas 104a, 104b, 104c. Each of these small areas can be served by each eNB subsystem. In 3GPP, the term “cell” can refer to the smallest coverage area of an eNB and / or eNB subsystem serving this coverage area. In other systems, the term “sector” can refer to the subsystem that serves this coverage area and / or the smallest coverage area. For clarity, the following description uses the 3PGG concept of cells.

  UE 120 may be distributed throughout the system. A UE may be fixed or mobile and may also be called a mobile station, a terminal, an access terminal, a subscriber unit, a station, and so on. The UE may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a laptop computer, a cordless phone, and so on. A UE may communicate with one or more eNBs by transmission on the downlink and uplink. The downlink (or forward link) refers to the communication link from the eNB to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the eNB. In FIG. 1, a solid line with two arrows indicates communication between the UE and the eNB. A dashed line with one arrow indicates a UE attempting to hand over to another eNB.

  A mobility management entity / system architecture evolution (MME / SAE) gateway 130 is connected to the eNBs 110 and may support communication for the UE 120. For example, the MME / SAE gateway 130, for example, for paging message delivery to the eNB, security control, idle state mobility control, SAE bearer control, higher layer signaling encryption and integrity protection, for paging reasons Various functions such as user plane packet suspension, user plane switching for UE mobility support can be performed. System 100 may include other network entities that support other functions. The network entity in LTE is a publicly available 3GPP entitled "Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description" in March 2007 It is described in TS 36.300.

  In the example shown in FIG. 1, the eNB 110a has three cells A1, B1, and C1 that cover different geographical areas. The eNB 110b also has three cells A2, B2, C2 that cover different geographical areas. The cells of eNBs 110a, 110b can operate at the same frequency. For clarity, FIG. 1 shows eNB cells that do not overlap each other. In a realistic configuration, adjacent cells of each eNB generally overlap each other at the edge. Further, each cell of each eNB typically overlaps one or more cells of one or more other eNBs at the edge. This overlap at the coverage edge ensures that the UE can receive coverage from one or more cells at any location as it moves around the system.

  FIG. 2 shows another configuration of the eNBs 110a and 110b. In the example illustrated in FIG. 2, the eNB 110a includes two cells A1 and B1 that operate in two frequencies F1 and F2, respectively, and have overlapping coverage areas. The eNB 110a also has two cells A2 and B2 that operate at two frequencies F1 and F2, respectively, and have overlapping coverage areas. The cells A1 and B1 overlap with the cells A2 and B2 at the ends, respectively, and the cells A2 and B2 overlap with the cells A1 and B1 at the ends, respectively.

  In general, an eNB may have any number of cells on any number of frequencies. Multiple cells may be deployed on different frequencies in a given geographic region to increase capacity. In this case, UEs in a geographical area can be distributed across cells on different frequencies in order to level the load between these cells. In general, a UE can perform a handover from a serving cell to a cell that can be better served by the UE. A better cell may be on the same frequency as the serving cell or on a different frequency.

  FIG. 3 shows a state diagram 300 for a UE in LTE. The UE may operate in one of several states, such as LTE detach state, LTE idle state, and LTE active state. When activated, the UE can enter the LTE detached state. In the LTE detached state, the UE has not accessed the system and is not known by the system. The UE performs initial system access and registers with this system. The UE then (i) either enters the LTE active state if the UE has data to exchange on the downlink or uplink, otherwise (ii) either enters the LTE idle state. Can be migrated.

  In the LTE idle state, the UE and system may have context information that allows the UE to quickly transition to the LTE active state. If there is data to transmit or receive while in the LTE idle state, the UE may perform random access and transition to the LTE active state. In the LTE active state, the UE may actively communicate with the system on the downlink and / or uplink. The UE can perform a handover to a new cell whenever it moves outside the coverage area of the serving cell. If the handover is successful, the UE remains in the LTE active state, and if the handover fails, the UE can return to the LTE idle state. The UE may also transition between various states in other ways.

  The system may support network initiated handover and / or UE initiated handover. In the case of a network initiated handover, the UE can perform a handover whenever directed by the system, and the system can, for example, determine whether the UE is based on measurements made by the UE and sent to a serving cell. A target cell to be handed over can be selected. For a handover initiated by a UE, also referred to as a forward handover, the UE can autonomously initiate a handover to the target cell.

  The UE can perform handover from the serving cell to the target cell in a cell-to-cell manner. In the case of inter-eNB handover, the serving cell is served by the source eNB, and the target cell is served by a target eNB different from the source eNB. Prior to the inter-eNB handover, the source eNB transfers the context information of the UE to the target eNB, and supports the target eNB serving the UE after the handover.

  The handover from the serving cell to the target cell may fail for various reasons. Since handover can be performed in a cell-to-cell manner, the UE can select the second target cell of the second target eNB if the handover to the original target cell fails. The UE can then attempt to re-establish the connection via the second target cell. This handover operation is considered to be unnecessarily complicated. This is because the UE context information needs to be transferred again from the source eNB to the second target eNB. To avoid this complexity, the UE disconnects from the source eNB and enters the LTE idle state. The UE then attempts to access the appropriate cell in the normal manner (eg, from the beginning) in the LTE idle state. However, if the handover fails, the service to the UE may be disrupted by the UE entering the LTE idle state.

  In an aspect, the UE can perform handover in a cell-to-eNB manner and perform handover of the target eNB to a different cell in order to increase the success probability of handover. The context information of the UE may be transferred from the source eNB to the target eNB by eNB-to-eNB communication. This context information can be easily transferred between different eNBs serving different cells of the target eNB. Thus, the UE can be handed over to any cell of the target eNB without having to perform another transfer of context information by the source eNB. Therefore, this cell-to-eNB handover technique makes the handover procedure robust by allowing the UE to select any cell of the target eNB without requiring additional overhead for the transfer of context information. Can increase the sex.

  The UE may obtain a list of candidate eNB candidate cells in various ways. These are candidates for handover. In one design, the source eNB sends a list of candidate cells to the UE, eg, by including the cell IDs of these cells in the handover command message to instruct the UE to perform a handover. be able to. The candidate cell may be geographically close to the serving cell of the UE. Candidate cells in the list are ordered, for example, starting with the cell that is most likely to be handed over to the cell that is least likely to be handed over. The UE can select one candidate cell from the list at a time starting from the first cell in the list to attempt a handover. Alternatively, the UE can select a candidate cell in the list to attempt a handover, for example, based on cell measurement results that are available at the UE. In general, the UE can autonomously select any candidate cell in the list and perform a handover initiated by the UE to the selected cell. If the handover to the selected cell fails, the UE can select another candidate cell in the list and attempt a handover to this cell.

  In another design, the UE may obtain a list of candidate eNB candidate cells from a neighbor cell list included in system information broadcast by the source eNB, target eNB, or other eNB. This neighbor cell list can include not only information associating these cells with the eNB, but also neighbor cells. For example, each cell in the neighbor cell list can be associated with a particular eNB ID. Alternatively, another set ID may be assigned to another eNB, and each cell may be mapped to the set ID of the eNB to which that cell belongs.

  In yet another design, the UE may obtain one or more lists of cells of one or more neighboring eNBs from measurement control messages sent by the source eNB. Based on the cell measurements reported by the UE, one of the neighboring eNBs is selected as the target eNB. The UE can then use the list of cells of the selected target eNB to attempt a handover. The UE may also obtain a list of candidate eNB candidate cells in another way.

  In one design, the source eNB may provide a list of candidate eNB candidate cells (e.g., in a handover command message) from which the UE may attempt handover. In another design, the source eNB may provide one target cell of the target eNB from which the UE can attempt a handover. If the handover to the target cell fails, the UE can autonomously attempt a handover to another cell of the target eNB. In yet another design, the source eNB provides one target cell of the target eNB from which the UE can attempt a handover and provides an indication of whether the UE-initiated handover is possible be able to. If the handover to the target cell fails and a handover initiated by the UE is possible, the UE can attempt a handover of the target eNB to another cell. The UE may also decide in another way whether to initiate a handover and / or to which cell to attempt the handover.

  FIG. 4 illustrates, for example, as shown in FIG. 1 or FIG. 2, from a source eNB serving cell to a target eNB cell, such as a UE 120 x handover from a cell A 1 of the source eNB 110 a to a cell of the target eNB 110 b FIG. 7 shows a design of a message flow 400 for UE inter-eNB handover. For clarity, only the signaling and functions appropriate for UE handover are described below.

  The UE first communicates with a service providing cell (eg, cell A1) of the source eNB. The source eNB sets up a measurement procedure for the UE (step 1), and the UE sends a measurement report to the source eNB (step 2). The source eNB decides to handoff the UE (step 3) and issues a handover request message to the target eNB (step 4). The source eNB sends the context information of the UE to the target eNB. This context information may include RRC context, SAE bearer context, and / or other information used to support UE communication. The target eNB can perform admission control and accept the UE handover (step 5). Thereafter, the target eNB can return a handover request acknowledgment (Ack) to the source eNB (step 6).

  Thereafter, the source eNB may send a handover command to the UE (step 7). The handover command may include one or more candidate cells (eg, cell A2 and cell B2 in FIG. 1 or FIG. 2) of the target eNB to which the UE can attempt a handover. The handover command may further include other information such as configuration information (eg, radio link configuration) for the target eNB. The UE can use this configuration information to send signaling to the target eNB.

  Thereafter, the UE can select a candidate cell (eg, cell A2) of the target eNB and perform random access using the selected cell to leave the source eNB and attempt a handover. For this random access, the UE can send a random access preamble to the selected cell via a random access channel (RACH) to synchronize to the selected cell ( Step 8). This selected cell may not be able to receive a random access preamble from the UE. Alternatively, the selected cell can receive a random access preamble and return a random access response, which may not be received by the UE. In any case, the UE may retransmit the random access preamble one or more additional times if it does not receive a random access response from the selected cell within a certain period of time. it can. If the UE does not receive a random access response after sending a random access preamble a specific number of times, it declares a handover failure for the selected cell. After declaring handover failure, the UE can select another candidate cell (eg, cell B2) of the target eNB and perform random access using this cell. The UE selects another candidate cell of the target eNB (i) until it receives a random access response from the selected cell, or (ii) all candidate cells of the target eNB are selected. And performing random access using the selected cell. The UE may receive a random access response from the target eNB candidate cell (eg, cell A2 or cell B2). The random access response may include information such as, for example, uplink (UL) response assignment, prior timing for the UE, and possibly other information.

  If the access to the target eNB candidate cell (eg, cell A2 or cell B2) is successful, the UE sends a handover confirmation message to this cell indicating that the UE's handover procedure is complete (step 10). The target eNB sends a handover complete message and notifies the MME / SAE gateway that the UE has changed the eNB (step 11). The MME / SAE gateway then switches the UE data path from the source eNB to the target eNB. The MME / SAE gateway also returns a handover complete Ack message to the target eNB (step 12). The target eNB sends a release resource message to the source eNB, indicating that the UE handover was successful (step 13). Upon receiving the release resource message, the source eNB releases resources for the UE (step 14).

  Each eNB may have a protocol stack that includes a non-access layer (NAS), radio resource control (RRC), medium access control (MAC), physical layer (PHY), and so on. The NAS can perform functions such as, for example, SAE bearer management, authentication, mobility handling and paging origination for idle UEs, and security control. The RRC may perform functions such as, for example, broadcast, paging, RRC connection management, radio bearer control, mobility function, and UE measurement reporting and control. The MAC may perform functions such as mapping between logical channels and transmission channels, data multiplexing and demultiplexing, and HARQ, for example. The PHY can perform the function of exchanging data via air. RRC is part of layer 3 (L3), RLC and MAC are part of layer 2 (L2), and PHY is part of layer 1 (L1).

  FIG. 5 illustrates, for example, as shown in FIG. 1 or FIG. 2, from a source eNB serving cell to a target eNB cell, such as a UE 120x handover from a cell A1 of the source eNB 110a to a cell of the target eNB 110b. FIG. 6 shows a design of a message flow 500 for UE inter-eNB handover. FIG. 5 shows PHY / MAC (L1 / L2) and RRC (L3) as separate entities for each eNB. FIG. 5 also shows signaling exchanged between the UE, L1 / L2 entity, and L3 entity at the source eNB and target eNB for handover.

  The UE can first communicate with a service providing cell (eg, cell A1) of the source eNB. The source eNB sets up a measurement procedure for the UE, and the UE can send a measurement report to the source eNB (step 2). The source eNB may decide to handoff the UE (step 3) and send the UE context information and a handover request message to the target eNB (step 4). The RRC at the target eNB sends a resource setup message to L1 / L2 at the target eNB (step 5). L1 / L2 executes admission control (step 6) and responds using resource setup Ack (step 7). The RRC at the target eNB can then return a handover response to the source eNB (step 8).

  The source eNB can then send a handover command to the UE (step 9). The handover command may include one or more candidate cells of the target eNB (eg, cell A2 and cell B2 of FIG. 1 or FIG. 2) that the UE can attempt to perform a handover. The UE may select one of the target eNB candidate cells (for example, A2) and perform random access using the selected cell (step 11). In step 11, the UE may send a random access preamble to the selected cell. The selected cell can respond by sending a random access response to the UE. The UE may not be able to receive a random access response from this selected cell. The UE can then select another candidate cell (eg, cell B2) for the target eNB and perform random access using this cell. Upon successful access to the target eNB candidate cell (eg, cell A2 or B2), the UE may send a handover complete message to this cell (step 12).

  The MME / SAE gateway receives a message to switch the UE data path from the source eNB (step 10) or from the target eNB (step 13). The MME / SAE gateway can then switch the UE's data path from the source eNB to the target eNB and return a release command to the source eNB (step 14). At the source eNB, the RRC can notify L1 / L2 to release the UE resources (step 15).

  FIG. 6 shows a design of a message flow 600 for UE inter-eNB handover from a serving cell of a source eNB to a target eNB cell. Message flow 600 may be a stand alone message flow or may be part of message flow 400 of FIG. 4 or message flow 500 of FIG.

  The UE can first communicate with a service providing cell (eg, cell A1) of the source eNB. The UE may send a measurement report to the source eNB (step 1). The source eNB may decide to handoff the UE and send the UE's context information and a handover request message to the target eNB (step 2). The target eNB can accept the handover and return a handover request Ack to the source eNB (step 3). The source eNB may then send a handover command to the UE along with a list of candidate eNB candidate cells (eg, cell A2 and cell B2) (step 4).

  The UE may select one candidate cell (eg, cell A2) in the list to attempt a handover. The UE may perform random access using the selected cell and send a random access preamble to this cell (step 5). The selected cell receives this random access preamble and responds by sending a random access response (step 6). The random access response can be erroneously decoded by the UE for various reasons. Alternatively, the random access preamble sent by the UE will be erroneously decoded by the selected cell and no random access response will be returned. In any case, the handover attempt to the selected cell fails.

  The UE then selects another candidate cell (eg, cell B2) in the list and attempts a handover. The UE performs random access using the selected cell and sends a random access preamble to this cell (step 7). The selected cell responds by receiving a random access preamble and sending a random access response. The random access response is correctly decoded by the UE (step 8). The UE then sends a handover confirmation message to the target eNB indicating that the UE handover procedure is complete (step 9). The UE can then communicate with this cell of the target eNB.

  As shown in FIG. 6, when the handover to the cell A2 fails, the UE can try the handover of the target eNB to the cell B2. If the UE has information indicating that cell B2 is a better cell, the UE can also directly attempt a handover to cell B2.

  4 to 6 show some examples of inter-eNB handover message flows. In general, inter-eNB handover may be performed using any set of messages based on any message flow. In the designs shown in FIGS. 4-6, the UE may attempt a UE-initiated handover to another cell of the target eNB. In another design, the target eNB cell may initiate a UE handover. For example, in response to receiving a handover request from the source eNB, the target eNB initiates a UE handover once for one cell, eg, by sending a message to the UE and monitoring the response from the UE Can be instructed to do.

The handover of the target eNB to any cell may be simpler than the handover of another eNB to the cell for the following reasons.
A given eNB cell generally has the same capacity and uses the same operating parameters. Thus, the radio link configuration in the handover command can be used for any cell of the same eNB.
-Resources are generally shared between cells of a given eNB. Thus, if the target eNB accepts the UE handover in the preparation phase, the target eNB will be able to serve the UE in any of the cells of the target eNB.
-Handover of the target eNB to any cell does not require an additional data path switch on the S1 interface between the eNB and the MME / SAE gateway.

  In other designs, the source eNB provides source eNB candidate cells for which the UE attempts handover. The candidate cell of the source eNB can give the UE more freedom when autonomously selecting a target cell for handover, and can increase handover reliability. The UE can select a target cell from among candidate cells of the target eNB and the source eNB based on various criteria. In one design, the UE may select a candidate cell with the best measurement and attempt a handover. In other designs, the UE may attempt a handover to all candidate cells of the target eNB before attempting a handover to the source eNB candidate cell. In another design, the UE may attempt a handover to all candidate cells of the source eNB before attempting a handover to the target eNB candidate cell. In any case, since the context information already exists in the source eNB, even if a handover to another cell of the source eNB is executed, the complexity does not increase from the viewpoint of UE context processing. Further, UE resources are generally not released by the source eNB until the handover procedure is completed, as shown in FIGS.

  The handover techniques described herein take advantage of the fact that UE context transfer is eNB-to-eNB communication while handover is a cell-to-cell mobility procedure. Thus, the UE is allowed to perform a handover to any cell of the target eNB and / or to any cell of the source eNB. Because it does not require an additional UE context transfer. This technique can improve handover reliability without incurring additional overhead for UE context transfer.

  FIG. 7 shows a design of a process 700 for performing a handover by a UE. The UE receives a handover command from the source base station (block 712). The UE attempts a handover from the source base station cell to the first cell of the target base station (block 714). If the target base station handover to the first cell fails, the UE attempts a handover of the target base station to the second cell (block 716). The source base station transfers the context information of the UE to the target base station for handover. This context information may be available to both the first cell and the second cell of the target base station without requiring another context transfer from the source base station.

  In block 714 and block 716, the UE may send a first random access preamble to that cell in order to attempt a handover of the target base station to the first cell. If the random access response from this cell is not received, the UE can determine that the handover to the first cell has failed. The UE may send a second random access preamble to that cell in order to attempt a handover of the target base station to the second cell. The UE can receive configuration information (eg, radio link configuration) of the target base station from the source base station (eg, by a handover command). The UE uses this configuration information to send a random access preamble and / or other signaling to the first cell and the second cell.

  In one design, the UE may receive the first cell and the second cell of the target base station from the source base station, eg, via a handover command or a measurement control message. In another design, the UE may receive only the first cell from the source base station and determine the second cell based on system information (eg, a neighbor cell list) broadcast by the source base station. it can. In another design, the UE receives a list of candidate cells for the target base station from the source base station, eg, based on measurements made by the UE, the first cell and the second cell from the list of candidate cells. Can be selected. The first cell and the second cell may cover another geographical area, for example as shown in FIG. Alternatively, the first cell and the second cell may operate at different frequencies and may have overlapping coverage areas, for example as shown in FIG.

  If the handover to the second cell fails and no other cell of the target base station is available to attempt the handover, the UE may transition to the idle state. The UE can attempt to hand over the source base station to another cell even if the handover to the second cell fails.

  FIG. 8 shows a design of an apparatus 800 that performs handover. Apparatus 800 includes means for receiving a handover command from a source base station (module 812), means for attempting a handover from a source base station cell to a first cell of a target base station (module 814), Means 816 for attempting a handover of the target base station to the second cell if the handover of the station to the first cell fails.

  FIG. 9 shows a design of a process 900 that supports UE handover by a source base station. The source base station sends a request for UE handover to the target base station (block 912) and sends the context information of the UE to the target base station (block 914). To initiate a handover of the UE to the target base station, the source base station may send a handover command to the UE (block 916). The UE may first attempt a handover of the target base station to the first cell, and if the handover to the first cell fails, it may then attempt a handover of the target base station to the second cell. it can.

  The source base station may send a measurement control message including a list of cells of the target base station to the UE. The source base station can receive measurement values made by the UE based on the measurement control message and select a target base station based on the measurement values. The source base station can send the first cell and the second cell of the target base station to the UE with a handover command, or only the first cell of the target base station. The source base station can also send configuration information of the target base station to the UE. The source base station can broadcast a neighbor cell list that includes the cells of the target base station.

  FIG. 10 shows a design of an apparatus 1000 that supports UE handover by a source base station. The apparatus 1000 starts means for sending a UE handover request to the target base station (module 1012), means for sending UE context information to the target base station (module 1014), and handover of the UE to the target base station. Means for sending a handover command to the UE (module 1016). Here, the UE first attempts a handover of the target base station to the first cell, and if the handover to the first cell fails, it then attempts a handover of the target base station to the second cell. .

  FIG. 11 shows a design of a process 1100 that supports UE handover by a target base station. The target base station receives a request for handover of the UE from the source base station to the target base station (block 1112). The target base station also receives context information for the UE from the source base station (block 1114). The target base station exchanges signaling with the UE for handover of the UE to the target base station (block 1116). The UE may first attempt a handover of the target base station to the first cell, and if the handover to the first cell fails, it may then attempt a handover of the target base station to the second cell. it can. If the UE handover to the first cell or the second cell is successful, the target base station may serve the UE based on the context information (block 1118).

  The target base station may receive a first random access preamble from the UE in the first cell and send a first random access response from the first cell to the UE. The first random access response may be erroneously decoded by the UE. The target base station may receive a second random access preamble from the UE and send a second random access response from the second cell to the UE in the second cell. Alternatively, the target base station erroneously decodes the first random access preamble sent by the UE to the first cell and the second random access preamble sent by the UE to the second cell. It can decode correctly and send a random access response from the second cell to the UE.

  FIG. 12 shows a design of an apparatus 1200 that supports UE handover by a target base station. Apparatus 1200 includes means for receiving a request for handover from a source base station of a UE to a target base station (module 1212), means for receiving context information of the UE from the source base station (module 1214), and a target of the UE Means (module 1216) for exchanging signaling with the UE for handover to the base station. Here, the UE first attempts a handover of the target base station to the first cell, and if the handover to the first cell fails, it then attempts a handover of the target base station to the second cell. . Apparatus 1200 further includes means (module 1218) for servicing the UE based on the context information if the UE handover to the first cell or the second cell is not successful.

  The modules in FIGS. 8, 10, and 12 may comprise processors, electronics devices, hardware devices, electronics components, logical circuits, memories, etc., or any combination thereof.

  FIG. 13 shows a block diagram of a design of UE 120, serving / source base station 110a, and target base station 110b. At base station 110a, transmit processor 1314a can receive traffic data from data source 1312a and signaling from controller / processor 1330a and scheduler 1334a. For example, the controller / processor 1330a may provide a message for UE 120 handover. Scheduler 1334a may provide allocation of downlink and / or uplink resources for UE 120. Transmit processor 1314a processes (eg, encodes, interleaves, and symbol maps) traffic data, signaling, and pilot and provides data symbols, signaling symbols, and pilot symbols, respectively. A modulator (MOD) 1316a performs modulation (eg, for OFDM) on these data symbols, signaling symbols, and pilot symbols and provides output chips. A transmitter (TMTR) 1318a adjusts (eg, analog converts, amplifies, filters, and upconverts) the output chip and generates a downlink signal. This is transmitted via the antenna 1320a.

  Base station 110b similarly processes signaling and traffic data for UEs served by base station 110b. Traffic data, signaling, and pilot may be processed by transmit processor 1314b, modulated by modulator 1316b, conditioned by transmitter 1318b, and transmitted via antenna 1320b.

  At UE 120, antenna 1352 receives downlink signals from base stations 110a, 110b and possibly other base stations. A receiver (RCVR) 1354 conditions (eg, filters, amplifies, downconverts, and digitizes) the received signal from antenna 1352 and provides samples. A demodulator (DEMOD) 1356 performs demodulation (eg, for OFDM) on the samples and provides symbol estimates. Receive processor 1358 processes (eg, symbol demaps, deinterleaves, and decodes) this symbol estimate and provides decoded data to data sink 1360. The decoded signaling is then provided to the controller / processor 1370.

  On the uplink, transmit processor 1382 receives and processes traffic data from data source 1380 and signaling (for random access, handover, etc.) from controller / processor 1370. A modulator 1384 performs modulation (eg, for SC-FDM) on the symbols from processor 1382 and provides output chips. The transmitter 1386 can adjust this output chip to generate an uplink signal. Uplink signals may be transmitted via antenna 1352. At each base station, uplink signals from UE 120 and other UEs are received by antenna 1320, conditioned by receiver 1340, demodulated by demodulator 1342, and processed by receive processor 1344. The processor 1344 provides the decoded data to the data sink 1346 and the decoded signaling to the controller / processor 1330.

  Controllers / processors 1330a, 1330b and 1370 direct the operation at base stations 110a and 110b and UE 120, respectively. Memories 1332a, 1332b, and 1372 may store data and program codes for base stations 110a, 110b, and UE 120, respectively. Schedulers 1334a and 1334b may schedule UEs for communication with base stations 110a and 110b, respectively, and allocate radio resources to the scheduled UEs.

  The processor of FIG. 13 may perform various functions for the handover techniques described herein. For example, a processor at UE 120 may perform process 700 in FIG. 7, UE process in message flows 400, 500, 600, and / or other processes for the techniques described herein. A processor at source base station 110a may perform process 900 in FIG. 9, processes for the source eNB in message flows 400, 500, 600, and / or other processes for the techniques described herein. it can. A processor at target base station 110b may perform process 1100 in FIG. 11, process for target eNB in message flows 400, 500, 600, and / or other processes for the techniques described herein. it can.

  Those skilled in the art will appreciate that these information and signals are represented using different techniques and techniques. For example, data, instruction groups, commands, information, signals, bits, symbols, and chips cited throughout the above description may be voltage, current, electromagnetic wave, magnetic field or magnetic particle, optical field or optical particle, or these It can be expressed by any combination.

  Those skilled in the art will further recognize that the various exemplary logic blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein are electronic hardware, computer software, or It will be understood that this is realized as a combination. To clearly illustrate the interchangeability between hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described generically in terms of their functionality. Whether these functions are implemented as hardware or software depends on the particular application and design constraints imposed on the overall system. Those skilled in the art can implement the functions described above in a manner that varies with each particular application. However, this application judgment should not be construed as causing a departure from the scope of the present invention.

  Various exemplary logic blocks, modules, and circuits described in connection with the disclosure herein are general purpose processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable devices. Implemented using a gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination of the above designed to implement the functions described above Or it can be implemented. A microprocessor can be used as the general-purpose processor, but instead a prior art processor, controller, microcontroller, or state machine can be used. The processor may be implemented as a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors connected to a DSP core, or any other such computing device combination. It is.

  The method or algorithm steps described in connection with the disclosure herein may be embodied directly by hardware, by software modules executed by a processor, or by a combination thereof. Software modules are stored in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, removable disk, CD-ROM, or other types of storage media known in the art. Can be done. A typical storage medium is coupled to the processor such that the processor can read information from, and write information to, the processor. In the alternative, the storage medium may be integral to the processor. The processor and storage medium can reside in the ASIC. The ASIC can also exist in the user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

  In one or more exemplary designs, the functions described can be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on a computer readable medium or transmitted by one or more instructions or code on a computer readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media may be in the form of RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage, or instructions or data structures. And any other medium used for transmitting or storing the desired program code means and accessible by a general purpose or special purpose computer, or a general purpose or special purpose processor. Also, any connection is properly referred to as a computer-readable medium. For example, the software may be a wireless technology such as infrared, wireless, and microwave, a digital subscriber line (DSL), a twisted pair, a fiber optic cable, a website using a coaxial cable, a server, Or, when transmitted from other remote sources, the definition of the medium includes radio technologies such as infrared, radio, and microwave, DSL, twisted pair, fiber optic cable, and coaxial cable. . As used herein, disks (disk and disc) include compact disks (CD), laser disks, optical disks, DVDs, floppy disks and blue ray disks. Normally, the disk magnetically reproduces data, and the disc optically reproduces data using a laser. Combinations of the above should also be included within the scope of computer-readable media.

  The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to these disclosures will also be apparent to those skilled in the art, and the general principles defined herein may be used in other variations without departing from the spirit or scope of the invention. Can be applied. Thus, the present disclosure is not intended to be limited to the examples and designs presented herein, but is intended to cover the widest scope consistent with the principles and novel features disclosed herein. Has been.

Claims (35)

A device for wireless communication,
If a handover of the user equipment (UE) from the source base station cell to the first cell of the target base station is attempted and the handover of the target base station to the first cell fails, the second of the target base station Comprising at least one processor configured to attempt a handover to another cell;
The source base station forwards the context information of the UE to the target base station for the handover;
The context information is available to both the first cell and the second cell of the target base station;
The apparatus further comprises a memory coupled to the at least one processor.   The at least one processor sends a first random access preamble to the first cell to attempt a handover of the target base station to a first cell, and a second cell of the target base station The apparatus of claim 1, configured to send a second random access preamble to the second cell to attempt a handover to the second cell.   The at least one processor is configured to determine that a handover of the target base station to the first cell has failed if no random access response is received from the first cell. Equipment.   The apparatus of claim 1, wherein the at least one processor is configured to receive a first cell and a second cell of the target base station from the source base station.   The at least one processor receives a first cell of the target base station from the source base station and determines a second cell of the target base station based on system information broadcast by the source base station. The apparatus of claim 1 configured to:   The at least one processor is configured to receive a list of candidate cells of the target base station from the source base station and select the first cell and the second cell from the list of candidate cells. The apparatus of claim 1.   The at least one processor is configured to first select the first cell based on a measurement value of the cell of the target base station, and then select a second cell based on the measurement value. The apparatus of claim 1.   The at least one processor receives configuration information of the target base station from the source base station and sends signaling to attempt handover to each cell of the target base station using the configuration information The apparatus of claim 1 configured as follows.   The apparatus of claim 1, wherein the first cell and the second cell of the target base station cover different geographical areas.   The apparatus of claim 1, wherein the first cell and the second cell of the target base station operate at different frequencies and have overlapping coverage areas.   The at least one processor is adapted to transition to an idle state if a handover of the target base station to a second cell fails and no other cell of the target base station is available to attempt the handover. The apparatus according to claim 1, which is configured as follows.   The apparatus of claim 1, wherein the at least one processor is configured to attempt a handover to another cell of the source base station if a handover of the target base station to a second cell fails. A method for wireless communication comprising:
Attempting a handover of the user equipment (UE) from the source base station cell to the first cell of the target base station;
When handover of the target base station to the first cell fails, attempting to hand over the target base station to the second cell,
The source base station forwards the context information of the UE to the target base station for the handover;
The method wherein the context information is available to both a first cell and a second cell of the target base station. Attempting a handover to the first cell comprises sending a first random access preamble to the first cell of the target base station to attempt a handover to the first cell;
Attempting a handover to the second cell comprises sending a second random access preamble to the second cell of the target base station to attempt a handover to the second cell. Item 14. The method according to Item 13.   The method of claim 13, further comprising receiving a first cell and a second cell of the target base station from the source base station. Receiving a first cell of the target base station from the source base station;
14. The method of claim 13, further comprising determining a second cell of the target base station based on system information broadcast by the source base station. A device for wireless communication,
Means for attempting a handover of user equipment (UE) from a cell of the source base station to a first cell of the target base station;
Means for attempting a handover of the target base station to the second cell if the handover of the target base station to the first cell fails;
The source base station forwards the context information of the UE to the target base station for the handover;
The context information is available to both the first cell and the second cell of the target base station. Means for attempting a handover to the first cell comprises means for sending a first random access preamble to the first cell of the target base station in order to attempt a handover to the first cell;
The means for attempting a handover to the second cell comprises means for sending a second random access preamble to the second cell of the target base station in order to attempt a handover to the second cell. Item 18. The device according to Item 17.   The apparatus of claim 17, further comprising means for receiving a first cell and a second cell of the target base station from the source base station. Means for receiving a first cell of the target base station from the source base station;
18. The apparatus of claim 17, further comprising means for determining a second cell of the target base station based on system information broadcast by the source base station. When executed by a machine, the machine
Attempting a handover of a user equipment (UE) from the source base station cell to the first cell of the target base station;
A machine-readable medium comprising instructions for executing an operation including a handover of the target base station to a first cell fails and an attempt to perform a handover of the target base station to a second cell. ,
The source base station forwards the context information of the UE to the target base station for the handover;
The context information is a machine readable medium that is available to both a first cell and a second cell of the target base station. A device for wireless communication,
A handover command for sending a user equipment (UE) handover request from a source base station to a target base station, sending context information of the UE to the target base station, and initiating a handover of the UE to the target base station; Comprising at least one processor configured to send to the UE;
The UE first attempts a handover of the target base station to a first cell, and then, if a handover to the first cell fails, attempts a handover of the target base station to a second cell;
The apparatus further comprises a memory coupled to the at least one processor.   23. The apparatus of claim 22, wherein the at least one processor is configured to send a first cell and a second cell of the target base station to the UE in the handover command.   The at least one processor is configured to send only the first cell of the target base station to the UE and broadcast a neighbor cell list comprising the cell of the target base station in the handover command The apparatus of claim 22.   The at least one processor is configured to send configuration information of the target base station to the UE, wherein the configuration information is used to send signaling for attempting a handover to each cell of the target base station. 23. The apparatus of claim 22, used by the UE.   The at least one processor sends a measurement control message comprising a list of cells of the target base station to the UE, receives measurements made by the UE based on the measurement control messages, and 23. The apparatus of claim 22, configured to select a target base station for handover of the UE based on. A method for wireless communication comprising:
Sending a user equipment (UE) handover request from a source base station to a target base station;
Sending context information of the UE to the target base station;
Sending a handover command to the UE to initiate a handover of the UE to a target base station,
The UE first attempts a handover of the target base station to a first cell, and then attempts a handover of the target base station to a second cell if the handover to the first cell fails .   28. The method of claim 27, further comprising sending a first cell and a second cell of the target base station to the UE with the handover command. Sending only the first cell of the target base station to the UE in the handover command;
28. The method of claim 27, further comprising broadcasting a neighbor cell list comprising a cell of the target base station. A device for wireless communication,
Receiving a request for handover of a user equipment (UE) from a source base station to a target base station, receiving context information of the UE from the source base station, and for handover of the UE to the target base station; Comprising at least one processor configured to exchange signaling with the UE;
The UE first attempts a handover of the target base station to a first cell, and then, when a handover to the first cell fails, attempts a handover of the target base station to a second cell,
The at least one processor is further configured to serve the UE based on the context information upon successful handover of the UE to the first cell or the second cell;
The apparatus further comprises a memory coupled to the at least one processor.   The at least one processor receives a first random access preamble from the UE in the first cell and sends a first random access response from the first cell to the UE; 31. The second cell is configured to receive a second random access preamble from the UE and send a second random access response from the second cell to the UE in the second cell. The device described in 1.   The at least one processor erroneously decodes a first random access preamble sent by the UE to the first cell, and a second random access preamble sent by the UE to the second cell. 31. The apparatus of claim 30, configured to correctly decode an access preamble and send a random access response from the second cell to the UE. A method for wireless communication comprising:
Receiving a user equipment (UE) handover request from a source base station to a target base station;
Receiving context information of the UE from the source base station;
Exchanging signaling with the UE for handover of the UE to the target base station,
The UE first attempts a handover of the target base station to a first cell, and then, when a handover to the first cell fails, attempts a handover of the target base station to a second cell,
The method further comprises servicing the UE based on the context information upon successful handover of the UE to the first cell or the second cell. For the handover, exchanging signaling with the UE
Receiving a first random access preamble from the UE in the first cell;
Sending a first random access response from the first cell to the UE;
Receiving, in the second cell, a second random access preamble from the UE;
34. The method of claim 33, comprising: sending a second random access response from the second cell to the UE. For the handover, exchanging signaling with the UE
Erroneously decoding a first random access preamble sent by the UE to the first cell;
Correctly decoding the second random access preamble sent by the UE to the second cell;
34. The method of claim 33, comprising sending a random access response from the second cell to the UE.

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